The Doctor's World; Technique Changes In Bypass Surgery

By LAWRENCE K. ALTMAN, M.D.

Published: August 9, 1988

HEART surgeons are increasingly turning to a new technique for coronary bypass surgery that promises longer-term success and fewer complications than the method that has been common for decades.

Rather than using sections of a leg vein to bypass blocked coronary arteries, the doctors are turning to a blood vessel in the chest.

For reasons that defy explanation, these blood vessels, internal mammary arteries, rarely develop the fatty deposits that characterize atherosclerosis, the artery-blocking condition that makes the surgery necessary in the first place.

Surgeons are using the arteries, also known as internal thoracic arteries, whenever possible in the operation that is commonly done to relieve the chest pains from angina. Men and women have two internal mammary arteries, one on each side behind the ribs near the breastbone.

The object of bypass surgery is to take a vessel from elsewhere in the body, sew it into a coronary artery to develop a flow of blood around the blocked area and to supply vital nutrients to the heart. But the benefits of the operation last only as long as the new vessels stay open.

Surgeons first turned to veins because they were more accessible and because efforts to use other arteries were generally unsuccessful for a variety of reasons. The saphenous veins of the leg became the standard. Other veins quickly took over their functions in the leg, just as other arteries take over the function of the internal mammary arteries that are removed in the newer procedure.

In many patients, vein grafts function well 15 or more years after the surgery.

But in other patients the grafts can have a more limited life span because the thinner walls of the veins are less able to withstand the pressures in an artery. Further, the transplanted veins can become blocked by plaques, much like the arteries they replace. Many bypass patients require another operation and in some cases suffer heart attacks and die.

The new wave of enthusiasm for internal mammary arteries reflects studies showing that grafts from these vessels can stay open much longer than those from leg veins. The studies have also found that patients who undergo such grafts live longer, take longer to develop recurrences of angina, have fewer heart attacks, fewer repeat bypass operations, and fewer complications than did those who had vein grafts.

Several decades ago doctors used internal mammary arteries in a different type of operation for angina, a generally unsuccessful one known as the Vineberg procedure. In the procedure, the mammary artery was linked directly to the heart muscle in hopes of increasing the blood flow to the heart.

The current use of internal mammary arteries for coronary bypass surgery was pioneered in the late 1960's by Dr. George E. Green, then at New York University and now at St. Luke's-Roosevelt Hospital Center in New York.

At the time, many experts believed that the internal mammary artery, often only two millimeters in diameter, was too small for splicing into the coronary arteries. But Dr. Green recalled in an interview that he shifted his research from other vessels to the internal mammary artery after another surgeon made him aware that ''the limiting factor was the eye, not the hand.'' By using the operating microscope to magnify the vessel, Dr. Green was able to accomplish the mammary artery graft successfully.

''Many years ago George Green stood alone in support of the internal mammary artery as a superior conduit,'' Dr. John L. Ochsner of the Ochsner Clinic in New Orleans has written. ''In the years since, many of us have joined his ranks.''

But they did so slowly. American surgeons used internal mammary arteries in 6,000 of 188,000 coronary bypass operations in 1983 and in 67,000 of 284,000 such operations in 1986, according to the American Heart Association. Several leading heart surgeons and cardiologists estimated in interviews that about 80 percent of coronary bypass operations now involve the use of internal mammary arteries or a combination of the artery and the vein. They cite favorable long-term results reported by groups such as those headed by Dr. Floyd D. Loop at the Cleveland Clinic and Dr. Airlie Cameron of St. Luke's-Roosevelt Hospital Center.

Internal mammary artery graft operations take longer and are technically more difficult than leg vein grafts. Surgeons, often aided by microscopes or magnifying loupes, must take care not to tear the small artery or its many tiny branches.

But even with these aids, a slight lapse in technique can produce poor results. Because the artery is so small, an improperly placed suture can narrow it enough to forever limit the blood flow.

Thus many surgeons wanted convincing data before they were willing to turn from vein grafts to the internal mammary artery grafts. It took years to do the studies that have shown the superiority of the newer technique. Along the way there was considerable debate. When only short-term results were available, the benefits of mammary artery grafts were only slightly better than those of vein grafts. But the benefits generally became clearer five or more years after the bypass operation.